Life refuses simple classification. As much as we would like like to draw a distinct line between life and non-life, it is usually not that simple  Much like how a platypus defies the typical notion of what a mammal is by it’s egg-laying nature, webbed feet and duck-like bill, life, even in its most fundamental basis, defies simplicity. If this is the case, what is the point of trying to define life? Creating a functional definition of life is a worthwhile effort because our definition of life influences how we search for extraterrestrial life and our behavior towards the unknown world.

Our understanding of life and how it originates dictates how we search for life beyond the Earth. Since all known life is carbon-based and dependent on liquid water, we began our search for habitable planets by assuming these features were prerequisites for life. In addition, we can conduct further testing to make a determination of possible lifeforms by using tests based on aspects fundamental to Earthly life, like genetic testing and metabolism tests. While this is a useful stepping stone, our knowledge of life shouldn’t restrict our endeavors as life may be vastly different elsewhere. Then, if we happen to find other samples of life, we can adjust our definition to include it. This way our definition is constantly evolving to more effectively find diverse life.

Regardless of whether something can be said to be objectively alive or not, our subjective beliefs about life determines our behavior towards it. Classifying something as alive requires that we give some amount of consideration and care in a way that would not be provided to non-life. It is therefore necessary that our definition of life be as current and accurate as possible. For example, assume we discovered a new planet full of rocks indistinguishable from the common rocks of Earth. We carelessly step over and on them with no regard to whether we disturb or break them. However, as we continue exploring we see the rocks appear to be moving, albeit at a incredibly slow rate. We would then be horrified as our actions may have injured or even killed these creatures which we would then consider alive. A similar case can and should be made concerning whether A.I. or advanced robots should also be considered alive as it will greatly affect how we treat them.


It is my belief that there will never be a perfect definition life that sufficiently classifies all possible forms of life and excludes non-life. If life originated independently elsewhere in the universe, it could easily completely upturn our understanding of life. However, it is still important that we retain a functional definition for life to help us find those beings we are able comprehend in an ethical way.


Benner, S. A. (2010). Defining Life. Astrobiology,10(10), 1021-1030.

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I really like how you brought up the fact that we could explore another planet and how we see life could be completely different from how the life is on other planets.  I also like how you stated that the definition needs to be flexible for life's that we do not expect to see. 

However, I think that it would exploring other planets that could very possibly have life on them would be bad because we would not know what bacteria are on their planet.  I think that even if we have a good definition of life, we still need to be cautious of what those other living things could hold. 

I find the part where you mention how we treat life and non-life different.  While I disagree that we don't cherish non-living objects, we do get stronger feelings from objects that we know are living.  I also agree that when AI is created, it will be a huge ethical issue whether or not we consider them alive and the consequences of that decision will be important.

I disagree that there needs to be a working definition, however.  In my opinion, a definition, currently, is not that important other than classifying new objects we find in the cosmos.  While I agree that we should keep an open mind regarding our discoveries, there's no real point in having any definition at all without more samples from different bodies in the universe


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